JetBrains Rider 2019.2 Help

Code Inspection: Use collection’s count property

If a collection has a Count property (or a Length property), JetBrains Rider suggests using the property instead of the Count() method. The property works faster (to see why, read the StackOverflow answers linked in the See Also below). Such a replacement is only possible for collections that implement ICollection<T> or its derived interfaces.

For arrays, JetBrains Rider suggests replacing Count() with Length:

Suboptimal code

After the quick-fix

public int BooksCount(string[] books) { return books.Count(); }
public int BooksCount(string[] books) { return books.Length; }

For other collection types, JetBrains Rider suggests replacing Count() with Count:

Suboptimal code

After the quick-fix

public int ToysCount(IList<string> toys) { return toys.Count(); }
public int ToysCount(IList<string> toys) { return toys.Count; }
Last modified: 20 August 2019

See Also